Head up display unit, liquid crystal display panel, and method of fabricating the liquid crystal display panel

ABSTRACT

A head up display unit equipped at least with transparent and flat image information display means, transparent and flat light irradiating means arranged in an opposed and close contact relationship with the image information display means, light supply means for supplying light to the light irradiating means, image-display control means for controlling image display, and light-supply control means for controlling light supply. The display unit is a compact head up display unit which can be used in any place in the interior of an automobile.

TECHNICAL FIELD

The present invention relates to a head up display where, in a vehiclesuch as an automobile, a ship, and a railroad vehicle, forwardexternal-scene information and various kinds of image and characterinformation from the interior are superimposed and looked at by anoperator (driver).

BACKGROUND ART

In vehicles, it is important from the point of view of safety that anoperator operating (driving) with his or her eyes forwardly fixed to thefront, when changing the visual point in an instant and looking at adisplay such as a velocity display, can accurately read out thedisplayed contents for the shortest possible time.

In recent years, in vehicles, particularly automobiles, there has been astrong movement to adopt a so-called "head up display (hereinafterreferred to as a HUD)" which has been developed in aircraft. In thisHUD, the displayed image of a CRT is projected on a combiner(semitransparent reflection plate) disposed at the front of a pilot'sseat (or on a windshield) with an optical system such as lenses,mirrors, and holograms, and is displayed in a form superimposed upon theforward scene. As a result, the HUD becomes a unit which makes itpossible to reduce movement of one's eyes or focusing as much aspossible and to enhance visibility.

In the railroad vehicles, there is plenty of space for housing an imagedisplay section, and as shown for example in Published Unexamined PatentApplication No. H4-110236, the image display section is comprised ofconsiderably large-scale devices such as a CRT, a lens, a mirror, and aconcave mirror.

On the other hand, in the automobiles, space for housing an imagedisplay section or an optical system is limited, and as shown forexample in U.S. Pat. No. 4,740,780, U.S. Pat. No. 4,664,475 or"Development of Hologram Head-up Display" (SAE TECHNICAL PAPER SERIES920600, (1992) by H. KATO et al.), liquid crystal or a LED is used asthe image display section and is combined with an optical system such asa mirror, and the combined unit is housed in a compact form in aninstrument panel. However, in order to form a focus at a great distance,the reflections at the mirrors are repeated to obtain a long opticalpath leading from the image display section to the combiner. For thisreason, a certain space has become necessary. Thus, these opticalsystems are housed in the instrument panel, but it is desirable that theuse of the space be avoided where various kinds of devices or wiring areclose together, and if possible, it is desirable that the use of thisspace be avoided. That is, a conventional HUD such as this is anexcellent display where the forward external scene and various kinds ofimage information and character information from the interior can besuperimposed and viewed at front of the driver's seat, but in order toachieve this, the conventional HUD has a large problem that aconsiderable space must be occupied.

This problem originates in the fact that the HUD takes the projectiontype display structure that the image generated in the image displaysection is projected and displayed on the combiner surface. The HUD, aspreviously described, is originally a system which has been developed inaircraft, and various functions that had been required in that case, asthey are, have been applied to vehicles, etc. Therefore, it isconsidered that the requirements which cannot always be said to beindispensable in vehicles have also been introduced as they are.

In aircraft, the forward view's space is a wide space where the field ofview is not much obstructed, and the operator is operating focusing thevisual point at the infinite point. Therefore, it is preferable that theimage of the HUD be also focused at the infinite point. In addition,even if considerably complicated information were displayed on thedisplay, it would not become an obstacle to the operation of theoperator, and conversely, the operator does need such complicatedinformation.

On the other hand, in vehicles, particularly automobiles, the driver isdriving, viewing about 10 to 20 m ahead, about 50 m ahead at the most.Also, the forward external scene is full of variety, and the operator islooking at an ever-changing sight, such as scenes, various kinds ofdisplay plates, and forward vehicles. If extremely complicatedinformation is displayed on the display, conversely it will become anobstacle to driving. When the driver looking about 20 m to the frontlooks at an image displayed between the driver and the front, it hasbeen said that the driver can recognize the image without difficulty ifthe focus is formed about several meters ahead. Furthermore, extremelyspeaking, it is considered that, as long as the forward scene and thedisplay information are superimposed and can be seen and in a case whereboth are in the field of view at the same time even if the displayinformation were not in the same focal distance as the forward scene,the forward scene and the display information can be read out withouthaving a feeling of incompatibility or fatigue so much, unlike lookingat the displays of the meters of a normal instrument panel section.

If a complicated and fine image is displayed, then a suitable imagedisplay device, i.e., a CRT, a TFT transmission liquid display, etc.,will be needed. In the present technique, it will be inevitable that thedisplay device will become a projection type in order to display theimage while superposing upon an external scene. In addition, in theprojection type, in order for an image to be formed so as to have afocus far ahead, an optical system such as a lens or a mirror willbecome necessary. However, if it is assumed that a complicated image isnot displayed unlike the aforementioned case, the limitation that a CRTis used in the image display section in order to make a projection typewill be removed, and it will become possible to drastically change theconcepts of the HUD.

As described above, in the automobiles, the space for housing an imagedisplay unit or an optical system is limited, and if possible, it isdesirable that the use of this space is be avoided. A method of solvingthis problem is by using a transparent and flat image display unit tomake a direct view type rather than the projection type, and byarranging this display unit in the vicinity of the windshield. If donelike this, the driver can superimpose and look at the forward externalscene and the display information at the same time and drive safely. Atthis time, what is necessary is that the image portion of this imagedisplay unit maintains a fixed brightness. A transparentelectro-luminescent display can be simply used but is extremelyexpensive, and a passive image display unit is practical. However, anillumination system is needed in order for making use of this displayunit, and this illumination system is also required to be transparentand flat.

DISCLOSURE OF THE INVENTION

While the conventional HUD has the drawback that it requires a largehousing space because of the structure, the object of the presentinvention is to provide a HUD where a substantially transparent display,an optical system, and an illumination system are united in a body andwhich is compact and makes a housing space unnecessary.

The present invention provides the following means in order to achievethe object.

That is, the present invention is a head up display unit comprising:transparent and flat image information display means; transparent andflat light irradiating means arranged in an opposed and close contactrelationship with said image information display means; light supplymeans for supplying light to said light irradiating means; image-displaycontrol means for controlling the image display of said imageinformation display means; and light-supply control means forcontrolling the light supply of said light supply means.

It is preferable that the transparent and flat image information displaymeans be a liquid crystal panel, particularly a polymer dispersed liquidcrystal panel. Also, an electric shutter comprising a ferroelectric thinmaterial is suitable. And, said transparent and flat light irradiatingmeans arranged in an opposed and close contact relationship with saidimage information display means is light irradiating means which hasoptical-path converting means for emitting incident light which wasincident from said light supply means arranged on part or all of theperipheral edge of said light irradiating means, in a surface directionof said light irradiating means. It is preferable that the optical-pathconverting means be a volume phase hologram, a phase diffraction gratingcomprising asymmetrical unevenness, or a half mirror. And, a lightsource itself emitting light, such as various kinds of lamps. Adischarge tube, an electro-luminescence, a plasma illuminant, a lightemitting diode, and a laser, can be used as the light supply means forsupplying light to said light irradiating means. Also, the light supplymeans may be light supply means comprising a phosphor and a light sourcewhich excites said phosphor, or may be light supply means comprising aphosphor, a light source which excites said phosphor, and an opticalfiber for guiding light from said light source. Furthermore, the lightsupply means may be provided with a light source, an optical fiber forguiding light from said light source, and optical-path converting meansfor changing the direction of the light emitted from the light source orthe optical fiber. A volume phase hologram having a function of the samekind as that used in the aforementioned light irradiating means, a phasediffraction grating, or a half mirror can be used as the optical-pathconverting means.

Also, it is particularly suitable for the present invention that theimage portion displayed in said image information display means is imageinformation display means having a light scattering ability. Animportant form of the present invention is to use a polymer dispersedliquid crystal as image information display means.

Also, it is important that the light irradiating means for illuminatingthe image information display portion is a surface illuminant which issubstantially transparent when viewed from the driver side and whicheffectively illuminates the image information display portion. The useof a hologram which is capable of arbitrarily setting the directions ofincident light and emitted light is effective. An important form of thepresent invention is to use a volume phase hologram as light irradiatingmeans.

Also, in order to obtain a much more compact device and a high luminanceof image display, it is possible to make a device equipped with bothimage information display means and light irradiating means. In order torealize a transparent and flat reflection display device of the directvision type where light utilization efficiency is high, the presentinventors have eagerly searched for the distribution state of thecomposite of a high polymer and liquid crystal composing a polymerdispersed liquid crystal. As a result, it has been found that a liquidcrystal display can be realized whose operation is entirely different inan improved distribution state from prior art and whose scatteringefficient is extremely high. The liquid crystal display comprises: twosubstrates having electrode layers, at least one of said substratesbeing transparent; and a light regulating layer composed essentially ofa liquid crystal phase and a high-polymer phase, interposed between thesubstrates. The liquid crystal and high-polymer phases of the lightregulating layer are essentially distributed as hologram patterns madeby object light and reference light reflected at a scattering surface.Because this novel polymer dispersed liquid crystal display itself has ahologram function, it serves both as the image information display meansand the light irradiating means of the present invention and is animportant form of the present invention. The light regulating layer is alight regulating layer comprising a combination of a liquid crystalphase and a high-polymer phase which vary including points where a valueof a refractive index of said liquid crystal phase with respect toincident light becomes equal to a refractive index of said high-polymerphase, when a voltage is applied and a refractive index of said liquidcrystal phase is varied. With this, the entire device can easily be madetransparent.

The information displayed on the HUD is not very complicatedinformation, but it is preferable that the image be colored. As one ofthe methods for achieving this, the optical-path converting means, inthe light irradiating means which is a volume phase hologram, may beconstituted by said volume phase hologram where holograms differ atevery section. This is one of the features of the present invention. Ina case where the light irradiating means having the optical-pathconverting means constituted by the holograms differing at every sectionis arranged in an opposed relationship with said image informationdisplay means, coloring can be easily realized if display is controlledso that fixed image information is displayed in correspondence with eachportion of the different holograms. As a finer form, the lightirradiating means comprises a light source, a transparent substrate, anda volume phase hologram formed on the transparent substrate. Thetricolor light, which is emitted from said light source and propagatesthrough the said substrate, is spaciously separated and focused by saidhologram and form light spot groups arrayed in the form of a mosaic on aplane. Also, a hologram, where tricolor dot patterns are shifted onepitch by one pitch and are multi-recorded, is regenerated with thetricolor light which is emitted from said light source and thenpropagates through said substrate, whereby groups of three color lightspots, arrayed in the form of a mosaic, are formed. Furthermore, thecolor of light is changed by alternately switching the colors of a lightsource in a time series manner or alternately switching a tricolorfilter in a time series manner, each color light is propagated through atransparent substrate, and color illumination light information foruniformly illuminating the transparent substrate surface, multi-recordedon the hologram, are regenerated, whereby tricolor illumination lightwhich is switched in a time series manner is formed. These aretechniques which can be utilized in common in a case where the imageinformation display means and the light irradiating means are separatelyformed and in a case where they are integrally formed.

In order to fabricate a liquid crystal display serving both as imageinformation display means and light irradiating means, a lightregulating layer precursor is interposed between two transparentsubstrates having electrode layers, the light regulating layer precursoressentially including (1) a liquid crystal material, (2) a monomerand/or oligomer, (3) a photopolymerization initiator system which isactivated by a chemical active radiant ray. Then, both reference lightof a coherent chemical active radiant ray and object light, where thesame radiant ray is reflected at a scattering reflection surface, areirradiated, in order to form in said light regulating layer precursor aninterference pattern forming a hologram. And, photopolymerization isperformed to form the display. In this case, the coherent lightreflected at the scattering reflection surface interferes with thecoherent light from the adjacent very small scattering surfaces, andconsequently, there is a high possibility that a noise grating isformed. In order to prevent this, the present invention uses a hologrampattern made by the object light obtained by irradiating laser light toa special scattering plate where very small scattering areas forrandomly scattering incident light are arrayed in the form of a mosaic.Also, said hologram pattern may be made with the object light passedthrough a pin hole array and reference light. Also, said hologrampattern may be made with the object light obtained by irradiatingS-polarization light and P-polarization light, laser light of differentwavelengths, or sets of incoherent laser light beams irradiated fromdifferent laser devices, arrayed in the form of a mosaic, to thescattering plate, or by passing these light beams through the pin holearray. Also, the said hologram may be formed over the entire surface ofsaid light regulating layer, with the object light obtained byirradiating laser light to a mask having a fine pattern and a scatteringsurface and by scanning coherent reference light in synchronization withthe object light.

The liquid crystal display serving both the image information displaymeans and the light irradiating means is equipped at least with saidliquid crystal display device, a signal generator for transmitting asignal such as an image to the display device, and a light source orlight supply means for supplying light to said liquid crystal displaydevice. This display forms an important form of the HUD of the presentinvention. This light source or light supply means is arranged on oneend of a transparent substrate constituting said liquid crystal display,and the hologram pattern of the light regulating layer is formed so thatthe light incident from the end of the transparent substrate scattersand reflects light in direction nearly perpendicular to the substratesurface. This is also included in the present invention.

Furthermore, the light irradiating means is functionally incorporated inthis liquid crystal display, and if light irradiating means having anoptical-path converting means such as a volume phase hologram, i.e., aflat illuminator is used together, the degree of freedom of thedirection of incident light will be enlarged and this embodiment willbecome more useful.

Incidentally, for the light irradiating means of the present invention,various modes are possible depending upon the direction of the lightdiffracted by the hologram.

As one of the various modes, a liquid crystal display comprises apolymer dispersed liquid crystal display device, a hologram arranged ona transparent substrate, and a light source. The polymer dispersedliquid crystal display device is illuminated by light of said lightsource which is incident from an end surface of said transparentsubstrate and which is emitted from a surface of said transparentsubstrate in an inclined direction by said hologram. With this, thelight or unnecessary light diffracted by the hologram is removed, andonly the light scattered by the polymer dispersed liquid crystal displaydevice will get to an observer.

Also, a liquid crystal display may comprise a polymer dispersed liquidcrystal panel containing a dichroic dye, a hologram provided on atransparent substrate, and a light source. Light is diffracted at apredetermined angle toward said liquid crystal panel by said hologramwhere the light from the light source is incident from the end surfaceof the transparent substrate, and said liquid crystal device isilluminated. A transparent substrate provided with a hologram is closelyarranged at the back of said polymer dispersed liquid crystal panelcontaining a dichroic dye, and said hologram is formed so thatdiffracted light is emitted obliquely with respect to the substrate,when light from the light source is incident. This case is useful as atransmission direct vision type. On the other hand, a transparentsubstrate provided with a hologram is placed at the front of said liquidcrystal panel. A light absorbing plate is additionally placed at theback of said polymer dispersed liquid crystal panel containing adichroic dye, and said hologram is formed so that diffracted light isnearly emitted in parallel to the substrate. This case is useful as areflection direct vision type.

In general, a reflection liquid crystal panel has a reflecting plate atthe back thereof and does not use a special light source. An image isviewed making use of surrounding light and the reflection efficiency isbad, so only a dark image is obtained. Therefore, if a display isconstituted by a reflection liquid crystal panel, a hologram arranged onthe front surface of the panel, and a light source, and if, when lightis irradiated to said hologram, said hologram is recorded so thatdiffracted light is emitted nearly perpendicularly toward the liquidcrystal panel, then there will be obtained a display where a brightimage is obtainable. This case is also a useful form of the presentinvention.

Because the HUD of the present invention is transparent and thin, it iseasily placed on a dashboard of an automobile, has a drive portion whichcan be pulled down before and after, and can be fixed at an arbitraryangle. Also, the HUD can be fixed by a freely rotatable fixing toolattached to the upper portion of a windshield of an automobile and canbe pulled down to the windshield surface when it is used. This isparticularly suitable in the case of the reflection display. Inaddition, the HUD is placed in the vicinity of a rear window of anautomobile and can display image information to the outside.Furthermore, the HUD can be used in part or all of a windshield of anautomobile. Likewise, the HUD can be used in part or all of a rearwindow of an automobile.

The HUD of the present invention has become a HUD where transparent andflat image information display means and an optical system such astransparent and flat light irradiating means are united in a body andwhich is compact and makes a housing space unnecessary. With this, abright image can be viewed superposing it upon external scenes.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the basic construction of a HUD of the present embodimentand an example of the HUD installed in an automobile.

FIG. 2 shows the basic construction of a HUD of the present embodimentand the example of the HUD installed in an automobile.

FIG. 3 shows the basic construction of a HUD of the present embodimentand an example of the HUD installed in an automobile.

FIG. 4 shows an example of the light irradiating means of the HUD of thepresent embodiment.

FIG. 5 shows the example of the light irradiating means of the HUD ofthe present embodiment.

FIG. 6 shows the example of the light irradiating means of the HUD ofthe present embodiment.

FIG. 7 shows the example of the light irradiating means of the HUD ofthe present embodiment.

FIG. 8 shows an example of the structure where the light irradiatingmeans of the HUD of the present embodiment is a volume phase hologramand the image information display means is high-polymer dispersed liquidcrystal.

FIG. 9 shows an example of the light supply means of the HUD of thepresent embodiment.

FIG. 10 shows an example of the light supply means of the HUD of thepresent embodiment.

FIG. 11 shows an example of the function of the HUD of the presentembodiment.

FIG. 12 shows an example of a mosaic tricolor spot group in a volumephase hologram of the light irradiating means of the present embodiment.

FIG. 13 shows the example of a mosaic tricolor spot group in a volumephase hologram of the light irradiating means of the present embodiment.

FIG. 14 shows the example of a mosaic tricolor spot group in a volumephase hologram of the light irradiating means of the present embodiment.

FIG. 15 shows a method of fabricating a mosaic tricolor spot group.

FIG. 16 shows the method of fabricating a mosaic tricolor spot group.

FIG. 17 shows the method of fabricating a mosaic tricolor spot group.

FIG. 18 shows a dot pattern of the same tricolor spot group.

FIG. 19 shows a dot pattern of the same tricolor spot group.

FIG. 20 shows a dot pattern of the same tricolor spot group.

FIG. 21 is a side view of a diagram useful for showing the production ofa hologram.

FIG. 22 shows a light source for emitting tricolor light.

FIG. 23 shows a light source for emitting tricolor light.

FIG. 24 shows an example of a structure used for enhancing theutilization efficiency of the diffracted light in the volume phasehologram.

FIG. 25 shows an example of a structure used for enhancing theutilization efficiency of the diffracted light in the volume phasehologram.

FIG. 26 shows an example of a structure used for enhancing theutilization efficiency of the diffracted light in the volume phasehologram.

FIG. 27 shows a construction example of an image display deviceconstructed by a combination of the reflection optical element of thepresent embodiment and a polymer dispersed liquid crystal display deviceusing back scattering.

FIG. 28 shows a construction example of an image display deviceconstructed by a combination of the reflection optical element of thepresent embodiment and a polymer dispersed liquid crystal display deviceusing back scattering.

FIG. 29 shows an example of an exposure system for fabricating a liquidcrystal display equipped with both image information display means andlight irradiating means.

FIG. 30 shows an example of the operation of the HUD using theaforementioned liquid crystal display device.

FIG. 31 shows an example of the operation of the HUD using theaforementioned liquid crystal display device.

FIG. 32 shows a square-hole pattern for coloration.

FIG. 33 shows a model diagram of an occurrence and suppression of anoise grating.

FIG. 34 shows a model diagram of an occurrence and suppression of anoise grating.

FIG. 35 shows a model diagram of an occurrence and suppression of anoise grating.

FIG. 36 is a diagram for explaining a method of fabricating a polymerdispersed liquid crystal layer by the use of a special scattering plateor a pin hole array.

FIG. 37 is a diagram for explaining a method of fabricating a polymerdispersed liquid crystal layer by the use of a special scattering plateor a pin hole array.

FIG. 38 is a diagram for explaining a method of fabricating a polymerdispersed liquid crystal layer by the use of a special scattering plateor a pin hole array.

FIG. 39 is a diagram for explaining a method of fabricating a polymerdispersed liquid crystal layer by the use of a special scattering plateor a pin hole array.

FIG. 40 is a diagram for explaining a method of fabricating a polymerdispersed liquid crystal layer by the use of a special scattering plateor a pin hole array.

FIG. 41 is a principle diagram for explaining the function of animproved volume phase edge-lit hologram in the present embodiment.

FIG. 42 is a principle diagram for explaining the function of animproved volume phase edge-lit hologram in the present embodiment.

FIG. 43 is a conceptional diagram of a head up display of polymerdispersed liquid crystal using dichroic dyes in the present embodiment.

FIG. 44 is a conceptional diagram of a head up display of polymerdispersed liquid crystal using dichroic dyes in the present embodiment.

FIG. 45 is a diagram showing a head up display device using a reflectionliquid crystal display of the present embodiment.

FIG. 46 is a diagram showing a head up display device using a reflectionliquid crystal display of the present embodiment.

FIG. 47 is a diagram showing a head up display device using a reflectionliquid crystal display of the present embodiment.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention unites in a body a display serving as an imageinformation display section and an optical system such as a lightirradiating section for applying light to the display, and provides acompact HUD which can be arranged and used directly on a windshield orin the vicinity. The invention will hereinafter be described in detailwith drawings and embodiments.

(A)

FIG. 2 shows an example of the HUD of this embodiment placed in theinterior of an automobile. In FIG. 2, reference numeral 1 is the HUD ofthis embodiment, 2 a windshield, 3 a conventional instrument displaysection at an instrument panel section, 4 a dashboard, and 5 a driver'sseat. FIG. 1 shows the basic construction of the HUD 1. 11 is atransparent and flat light irradiating means section, 12 a transparentand flat image information display means section, 15 a light supplymeans section, 13 a control unit, and 14 a connecting cable. Because theHUD of this embodiment can be fabricated into a transparent and thintype, it does not become any obstacle of the visual field even when thedriver sitting on the driver's seat 5 shown in FIG. 2 is looking atforward external scenes. In FIG. 2 the HUD 1 is placed in the vicinityof the windshield and in front of the driver, so the display informationcan be read out superposing it upon forward external scenes. Since theHUD 1 is connected to the control unit 13 and the cable 14 and is astand-alone type, it can be set in an arbitrary place. Reference numeral1' indicated by a dotted line of FIG. 2 is an example of installationwhere the HUD is attached like a sunvisor and is pulled down forward ofthe driver's seat as needed. FIG. 3 shows other examples ofinstallation, and 31 of (a) is a case where movable sections areprovided in the left and right bottom portions of the HUD and where theHUD is placed on to the frame portion in front of the driver's seat sothat it can be used pulling down before and after, and the HUD can beput up at an arbitrary angle and used when necessary, and can be putdown when unnecessary. Also, 32 of (b) is a structure where the HUDsection is attached directly to the windshield and is a type which takesthe least space. Furthermore, it is also easy for those having skill inthis field to incorporate this HUD into a laminated glass as part of thewindshield, or the HUD itself becomes a windshield and the whole windowcan also be used as an image display section.

In order to install the image display means 12 on the windshield of anautomobile or in the vicinity and to display image information whilesuperposing it upon external scenes, a transparent display with acertain light transmittance is required as the image display means 12. Apassive display, such as an electro-chromic display (ECD), a liquidcrystal display (LCD), a dichroic-particle scattered display (DSD), aferroelectric thin-film display (FED), and a ferromagnetic display(FMD), can be used as the image display means. Among these, LCDs andFEDs are more suitable, considering durability, cost, and temperaturecharacteristic. If these transparent displays are placed in front of thedriver's seat and a forward external scene is superimposed and observedby the driver, then character information on the display, for example,can be recognized through external light. However, since this case (LCD,etc.) uses a polarizing plate, the transmittance is generally reduced,and this case depends upon the brightness of external light, so the highcontrast is difficult to obtain. Also, naturally, an image cannot beviewed during night, or where there is no light, such as a tunnel.Therefore, there is a method where a lamp placed in a suitable positionin an automobile is used as a light source for irradiating light towarda display, but there is a high possibility that the relative positionbetween the display and the light source will be fixed and that awasteful space will take place. Therefore, it is most desirable that adisplay and an illumination device consisting of light irradiating meansand light supply means be united in a body, as in the case of theembodiment of the present invention. The properties of this illuminationdevice requires that the device be transparent, that the incident lightfrom part or all of the end surface of the light irradiating means beirradiated toward the display and the irradiation of the light in theopposite direction be extremely small, and that the reflected light atthe display surface and the transmitted light from the external scene besufficiently passed through.

As one of the light irradiating means meeting such requirements, thereis a surface illuminant using holography. FIGS. 4 to 7 show the conceptsof the surface illuminant. When a hologram is generated, simplecollimated light is used in FIG. 4 as object light, instead of using thereflected light of the light irradiated to an actual object surface. Thecollimated light is irradiated perpendicular to a hologramphotosensitive body surface 41, and reference light is irradiated at anangle nearly perpendicular to this collimated light, thereby generatinga hologram. 42 is, for example, a transparent acrylic plate. Anillumination device, formed integrally with a light source as a normalholography for displaying a three-dimensional image rather than asurface illuminant like this embodiment of the present invention, hasbeen proposed by A. S. Benton et al. ("Edge-Lit Rainbow Holograms,"SPIE, Vol., 1212, pp. 149-157, 1990). The surface illuminant of thisembodiment can be fabricated by the same method, except that collimatedlight is utilized without using an actual object, as described above.FIG. 5 shows a hologram made in this way, and if white light isintroduced from the bottom portion (from the direction of the referencelight), it will be diffracted at a hologram surface at 43 and will beemitted in a direction nearly perpendicular to the surface (direction ofobject light). It is preferable that this hologram be made in a volumephase type. That is, a photosensitive resin whose refractive index isvaried by light irradiation is used, and a phase distributioncorresponding to a light intensity distribution of an interferencefringe is realized. Therefore, the diffraction efficiency is high andthe direction perpendicular to the surface is nearly transparent.External light is transmitted through without undergoing any influences,and the driver can look at an external scene as if looking throughnormal glass. The light emitted from this illumination device strikesupon a display surface which is placed in an opposed relationship withthe illumination device and then is reflected. FIG. 8 illustrates thisstate. It is desirable that the displayed image of a display at 52 be ascattering type, and among LCDs, polymer dispersed liquid crystal isparticularly desirable. The polymer dispersed liquid crystal is madefrom the structure where liquid crystal is scattered into a high-polymermatrix. The polymer dispersed liquid crystal becomes transparent when anelectric field is applied, and reaches an opaque scattering state 53when an electric field is off. This is not limited to polymer dispersedliquid crystal, but whatever capsules liquid crystal or whatever becomesa scattering type can be used. Because these displays are used withoutemploying a polarizing plate, a particularly bright image is obtained.The light incident upon the display surface, as shown in FIG. 8, isscattered at an image displaying portion 53 and is reflected in equaldirections. The reflected light passes in part through the hologram andis diffracted in the direction of the light source, but the reflectedlight has the excellent characteristic that the greater part thereof istransmitted through toward the driver side and is observed as a brightimage, because the reflected light has become scattered light.

For this light irradiating means, the aforementioned hologram is one ofthe most suitable means, but some other methods can be utilized. Thatis, the function of the light irradiating means, as previouslydescribed, is that the device is transparent, that the light incidentupon the end surface of the light irradiating means is converted inoptical path and is irradiated to the direction of the display, that theirradiation of the light to the opposite direction is extremely small,and that the reflected light from the display surface is sufficientlytransmitted through. Therefore, whatever meets these functions can beutilized. For example, what is shown in FIG. 6 is called a waveguidehologram or a grating coupler and is art known to those having skill inthis field. A diffraction grating 61 is provided on the surface of afilm 62 arranged on a transparent support (glass, for example) 63. Bymaking the refractive index of the film 62 greater than that of thesupport 63 and that of the air on the surface, the light introduced tothe film 62 in a fixed direction will meet total-reflection requirementsand can be propagated through the film. The so-called evanescent lightwhich has reached the diffraction grating section interacts with thediffraction grating, thereby emitting light to the outside. Bycontrolling the spaces of the diffraction grating, light can be takenout in a nearly perpendicular direction. Although, in general, thisdiffracted light is emitted in up and down directions as shown in theleft portion of FIG. 6, it was possible, according to this embodiment,that the most part of the diffracted light were emitted in onedirection, by forming the shape of the diffraction grating into anasymmetrical shape such as a sawtooth shape (right portion). Thisdiffraction grating made by holography is called a waveguide hologram.In addition, in FIG. 7 a half mirror 73 interposed between twotransparent support plates 71 and 72 is shown as a simpler method. Theincident light introduced from the bottom is reflected in part at thehalf mirror and is emitted in the surface direction. If the angle of thehalf mirror is set, for example, to 45 degrees, then the reflected lightcan be taken out in the direction perpendicular to the surface. Theremaining light is transmitted through the half mirror and reaches thenext half mirror. This operation is repeated and light is sequentiallytaken out in the surface direction, so the half mirror functions as atransparent surface illuminant.

For the light supply means (15 of FIG. 1) for supplying light to theaforementioned light irradiating means, light sources of any types wherethe source itself emits light, such as various kinds of lamps, adischarge tubes, electroluminescence, a plasma illuminant, a LED, and alaser, can be used. Also, as shown in FIG. 9, light is guided with anoptical fiber 81 connected to a suitable light source, and the light isirradiated through an optical system 82 (lens, prism, etc.) to aphosphor 83 in a fixed direction or as a magnified light beam, wherebythe light can also be supplied in the direction of 42. It is alsopossible to directly connect a light source instead of the opticalfiber. As another example, as shown in FIG. 10, light is introduced inthe same way as FIG. 9. In this case, optical-path converting means 91having the same function as the aforementioned light irradiating meansis used, whereby it can be operated as a light source with respect to42. Now, for the HUD of the embodiment of the present invention, anexample of the operation will be described.

(Embodiment-A1)

In FIG. 11, 101 is a polymer dispersed liquid crystal panel. Liquidcrystal/monomer/prepolymer (for example, E-8/2-ethyl hexylacrylate/urethane acrylate oligomer, made by BDH) is sandwiched betweenglass substrates having transparent electrodes, a photopolymerizationinitiator is added, and photopolymerization is carried out with UVlight, whereby the polymer dispersed liquid crystal panel was obtained.The entire size of the panel was set to 21 cm×16 cm×0.2 cm. The displayportion is segmented into three zones, and the electrodes are patternedso that "Divergence after xx m" is displayed on 102, symbols of anintersection and an arrow are displayed on 103, and speed such as "ΔΔkm"is displayed on 104. In the portion of the zone of 102, where thedisplay changes, there are only numerical characters representative ofdistance, and the other portions are fixed. In the zone of 103, symbolsof an intersection and arrows have been displayed, and they will change,for example, with a simple line display such as shown by dotted lines.Also, in the zone of 104, numerical characters representative of speedwill change. A simple character display such as this does not require adot matrix, a simple pattern can be used for the electrodes, and wiringcan be easily taken out by using the peripheral portion of liquidcrystal. 105 is an electrode wiring lead socket, and 106 is a lead cableconnected to the control device. 107 is a surface illuminant usingholography. For example, a piece of Dupont HRF-700 sheet is stacked upona glass plate (or acrylic plate) of thickness 0.4 cm as a photosensitivebody, and collimated light and reference light are irradiated aspreviously described. In this way, a hologram was made. At this time,the photosensitive sheet is segmented into three zones 108, 109, and110, as shown, and when making holograms, the photosensitive sheet isexposed with three light sources which is different in wavelength. Inthis way, three kinds of holograms are made on a single surfaceilluminant. These zones correspond to the zones 102, 103, and 104 ofliquid crystal. 111 is a light source, and a cold cathode FL lamp wasused. 112 is a reflecting plate, and 113 is a light source cable, whichis coupled to a controller that controls the on-off of light and lightregulation. 101 and 107 are superimposed to make a HUD. If 111 is lit,the zones of 108, 109, and 110 will respectively irradiate light beamsof different wavelengths toward the liquid crystal surface. That is,there becomes a tricolor display whose color differs at every zone. Thisliquid crystal is transparent at the time of voltage application, and animage is displayed in the off state of the liquid crystal. Therefore,first the liquid crystal is set to the ON state at the time of operationand then is set to the OFF state according to an image signal. If thelight source is lit with the liquid crystal in the transparent state,the light irradiated from 107 will pass through the transparent liquidcrystal and be emitted to the outside, and the liquid crystal remainstransparent when it is viewed from the internal driver. If, inaccordance with the characters of an image, a signal is sent from theimage control section and the liquid crystal is set to the OFF state ,the image will be displayed as a scattering surface. Then, the lightirradiated from 107 strikes upon the scattering surface and isreflected, and the image displayed in three colors at every zone isbrightly observed to the driver. For the external scene, the liquidcrystal is transparent except for the scattering surface of the liquidcrystal and therefore the image superimposed upon the external scene isseen. If the aforementioned zone is further segmented, it will also bepossible to display each character of each image with a different color.The aforementioned HUD is the simplest form of this embodiment and thebasic operation has been illustrated. As has already been described indetail, this HUD can be made more compact and can be operated withbright display, by combining various kinds of image information displaymeans, light irradiating means, and light supply means.

The HUD of this embodiment makes not only various displays in front ofthe driver's seat, but also if it is placed in the rear widow portionand used, it can be utilized as an effective warning with respect to thefollowing vehicles, i.e., as a so-called center high mount stop lamp.Also, it can be used as an information transfer display. At this time,if the surface illuminant is directed toward the vehicle inner side,then a white display image will be seen from the following vehicle as ifit floats on the bright display, and it will become a display whosevisibility is excellent. Of course, it is possible that the HUD will beused in part or all of the rear window.

(B)

Next, a description will be made of a general method of coloring thehead up display of this embodiment. As already described, it is easy tocolor the zones at every character. A description will hereinafter bemade in detail of the case of a finer image. In this case, the hologramas light irradiating means, which is used in this embodiment, isutilized. This hologram is transparent in external appearance and isreferred to as an optical element for applying colors of red, green, andblue to each pixel of the display device. With a combination of thisoptical element and the polymer dispersed liquid crystal display device,there can be provided a unit which is transparent, is capable of a colordisplay, and is a direct visual type.

(Embodiment-B1)

FIG. 12 is a principle diagram of the optical element in thisembodiment, FIG. 13 a diagram showing the function of the minimum unitarea of the hologram, and FIG. 14 a birds-eye view of the wholehologram. In FIG. 12, 121 is a volume phase hologram, 122 a transparentsubstrate, and 123 a light source. The hologram 121 has a function ofconverting the light from the light source 123 into a light spot groupwhere red, green and blue are regularly arrayed. Three elementholograms, which diffract light of three colors in different directionsand focus the light, are multi-recorded on the minimum unit area 124 ofthe volume phase hologram shown in FIG. 13. For the diffractiondirection by each color element hologram, a vertical direction such asthat shown in FIG. 13(a) or a horizontal direction such as that shown inFIG. 13(b) can be taken as an example, but the diffraction direction isnot limited to these directions. As shown in FIG. 14, a large number ofminimum unit areas 124 exist in the hologram 121, and they are adjacentto or overlapped with one another. As a consequence, the minimum unitareas 124 are disposed so that the regenerated light becomes a mosaictricolor light spot group on the focus surface. Each element hologram isregenerated only by both the light of the color used when recording andthe light having a wavelength in the vicinity of the color, but it isnot regenerated by light of a color different from that. This is acharacteristic found only in the volume phase hologram. Next, adescription will be made of the fabrication process of the hologram. InFIG. 15, 122 is a transparent substrate, 125 a hologram recordingmaterial, 126 a protective film of the hologram recording material, 127a lens let array, 128 recording light, and 129 reference light. FIGS. 16and 17 are views showing part of FIG. 15 on an enlarged scale. Thehologram recording material 125 is coated between the transparentsubstrate 122 and the protective film 126. For the recording material ofthe hologram, a photopolymer or gelatin bichromate, where highdiffraction efficiency is obtained and where there is less noise light,is suitable. In this embodiment, a photopolymer was used. First, therecording light 128, which is, for example, red laser light, is focusedby the lens let array 127. This state is shown in FIG. 16 on an enlargedscale. While in FIG. 16 the recording light has been illustrated so asto be irradiated horizontally, this embodiment is not limited to this.The hologram recording material 125 is put between the lens let array127 and the focal plane. Thus, a light intensity pattern caused by theinterference with the reference light 129 of the same color is recordedon the hologram recording material 125 as a refractive index profile.Now, if the recorded pattern is regenerated by irradiating light at aregenerative-light optical path 130 of the same optical path as thereference light 129, a red light spot group arrayed at the intervals ofsame cycle as the basic cycle "d" of the lens let array 127 will beformed on a single plane 131. In order for the regenerated light spotgroup to be disposed at very fine intervals of "p" from the point ofview of formation of a color image, the lens let array 127 is shifted atintervals of a fixed distance "p" and the recording process is furtherrepeated. This process is repeated d/p times. Next, this process isrepeated with a green laser beam. At this time, as shown in FIG. 17, theangle of incidence of the recording light 128' is slightly inclined sothat a green light spot to be regenerated is adjacent to the previouslyrecorded red light spot. Then, this process is repeated with a bluelaser beam. Likewise, the angle of incidence of the recording light isslightly inclined so that a blue light spot is adjacent to thepreviously recorded red light spot group and green light spot group. Forthe hologram 121 thus formed, respective colors are independentlyregenerated by irradiating tricolor light of red, green, and blue at theregenerative-light optical path 130 of the same optical path as thereference light 129, and the respective colors are diffracted atrespective different angles and are space-separated. Clear tricolorlight spot groups which are arrayed in a mosaic manner are formed on asingle plane and yet are transparent in external appearance.

(Embodiment-B2)

FIG. 18 is a birds-eye view of the multi-recorded hologram and the imageformation surface in this embodiment. The entire construction is thesame as FIG. 12 shown in the embodiment-B1. The basic pattern is a dotpattern such as the one shown in FIG. 19, and the basic patterns areshifted at intervals of one pitch so that they are overlapped with oneanother and recorded with red, green, and blue light. In the interior ofthe hologram, the three patterns are recorded as shown in FIG. 18, inthe form such that they share the space in the medium with one another.

For each pattern, the color dot patterns are regenerated independent ofeach other only by light of the color used when recording and lighthaving a wavelength in the vicinity of the color, and a tricolor lightspot group is formed on an image formation surface, as shown in FIG. 20.In FIG. 21, 122 is a transparent substrate, 125 a hologram recordingmaterial, 126 a protective film of the hologram recording material, 133a glass block, 134 an index matching solvent, 135 a pattern mask, 128recording light, and 129 reference light. It is desirable that the indexmatching solvent 134 be sandwiched between the protective film 126 andthe glass block 133. The pattern mask 135 on which dot patterns to berecorded are formed is fixed in the proximity of the transparentsubstrate 122 and is illuminated by the recording light 128 which is,for example, red laser light. At the same time as this, the referencelight 129 is incident from the side of the glass block 133, and thelight intensity pattern caused by the interference with the recordinglight is recorded on the hologram recording material 125 as a refractiveindex profile. For the mask pattern 135 used in this embodiment, thebasic pattern shown in FIG. 19, for example, is formed by boring holesin a thin metal plate, or a coated metal film is patterned on a glasssubstrate by photolithography. Then, the pattern mask 135 is shifted byone dot and is fixed, and pattern recording is likewise performed withgreen laser light. Furthermore, this process is repeated with blue laserlight. In addition to the recording method shown in this embodiment, ofcourse a multi-step method which is generally used as holography canalso be used. For the hologram 121' thus formed, the glass block isremoved and then respective colors are independently regenerated byirradiating tricolor light of red, green, and blue into the transparentsubstrate 122 at the regenerative-light optical path 130 opposed to thereference light 129. A clear tricolor light dot pattern is formed at aposition where the pattern mask 135 is placed when recording, and yet istransparent in external appearance.

(Embodiment-B3)

In this embodiment, the light source 123, as shown in FIGS. 22 and 23,can switch red, green, and blue colors, or comprises a combination of awhite light source and a tricolor filter and has a function of switchinga color in a time series manner.

On the volume phase hologram 121, three element holograms whichrespectively diffract light beams of three colors in certain directionsare multi-recorded so that they share the space in the medium with oneanother. The diffraction angles may be the same or different between thecolors. Each element hologram is regenerated only by light of the colorused when recording and light having a wavelength in the vicinity of thecolor, but it is not regenerated by light of a color different fromthat. The light of each color, emitted from the light source 123 andpropagated through the transparent substrate 122, regenerates eachelement hologram independently, and this regenerated light is emittedfrom the transparent substrate surface at respective certain angles, andbecomes uniform illumination light of each color. First, a lightintensity pattern, caused by the interference between the recordinglight 128 which is, for example, red laser light and the reference light129 of the same color, is recorded on the hologram recording material125 as a refractive index profile. The reference light 129 is collimatedlight or nearly collimated light, and the regenerated light becomes thesame collimated light or nearly collimated light. This process issubsequently repeated with green laser light and furthermore with bluelaser light. The hologram 121 thus formed is independently regeneratedwith tricolor light of red, green, and blue, which is incident at theregenerative-light optical path 130 of the same optical path as thereference light 129. Now, light of each color is alternately incident toregenerate each element hologram by switching the color of the lightsource or the color filter, and consequently, there is obtained uniformillumination light of three colors which alternately switch in a timeseries manner. Note that, when each element hologram is regenerated atthe same time with tricolor light without switching a color, whiteillumination light is obtained.

In the aforementioned embodiments of B1 to B3, as shown in FIG. 24 adifference between the diffraction efficiencies in the polarizationdirection of the regenerative light is improved and high efficiency oflight utilization can be realized, by selecting the angle between theregenerative-light optical path and the recording light so that itbecomes greater than 90 degrees after the incidence of the recordinglight upon the transparent substrate. At the same time, the influence ofthe scattering of the diffracted light, which is caused by the fact thatthe wavelength of the regenerative light has a certain width, can bereduced, and a clear dot pattern having no dimness can be regenerated.Also, uniform illumination light with no discolored portion is obtained.This does not need to be considered in a case where a light sourcehaving a single wavelength and a uniform polarization direction, such asa laser, is used, but it becomes important when regeneration isperformed with white light. In addition, the leakage of light from thesurface can be eliminated by selecting the regenerative-light opticalpath so that the regenerative light being propagated can meettotal-reflection requirements at the internal surface of the transparentsubstrate. Furthermore, as shown in FIGS. 25 and 26, if another end,which opposes the end on which the regenerative light is incident, isground like a prism and the vertical angle is made so that the remainingregenerative light, diffracted by the hologram, is all reflected andreturns back to the original optical path, then the leakage of lightfrom the end face can be eliminated. For example, the reflected lightmay be returned to the light source side in parallel to the surface ofthe transparent substrate (FIG. 25), or the vertical angle may be made90 degrees so that the reflected light is returned through the originalpath again to the light source side (FIG. 26).

In addition, while this embodiment has been described with reference tothe reflection hologram, the same function can be realized also for atransmission hologram.

Next, a description will be made of embodiments of application of thisinvention to a HUD.

(Embodiment-B4)

FIG. 27 is a schematic view of this embodiment, which is constructed bya combination of an optical element 144 forming the tricolor light spotsof the aforementioned embodiment and a polymer dispersed liquid crystaldisplay device 145. The optical element 144 in this embodiment isconstructed with a reflection hologram. The polymer dispersed liquidcrystal display device 145 displays an image, using the back scatteringof the liquid crystal layer.

(Embodiment-B5)

FIG. 28 is a schematic view of another embodiment of the presentinvention and is an example of the structure where an optical element146 forming the illumination light of the aforementioned embodimentwhere a color is switched in a time series manner and a polymerdispersed liquid crystal display device 145 are combined. The opticalelement 146 in this embodiment is constructed with a reflectionhologram. The polymer dispersed liquid crystal display device 145displays an image, using the back scattering of the liquid crystallayer. Illumination light of three colors which switches in a timeseries manner is supplied by fixing the polymer dispersed liquid crystaldisplay device 145 in the proximity of the optical element 146. Forexample, the switching is performed one time per 1/180 second, and theluminance signals corresponding to respective color images are displayedin synchronization with the aforementioned display device 145, whereby acontinuous color image is recognized by the eyes. While in theaforementioned embodiment a single color image has been constructed withthree pixels, in this embodiment the pixels of the polymer dispersedliquid crystal display device 145 can be all utilized in the imagedisplay and therefore the resolution is enhanced.

Any of the optical elements of this embodiment described above has beenconstructed by the reflection hologram, and any of the polymer dispersedliquid crystal display devices displays an image, using back scattering.However, a transmission hologram and a polymer dispersed liquid crystaldisplay device displaying an image by use of forward scattering may beused, and the combination thereof can be arbitrarily selected accordingto the purpose.

(C)

Next, a description will be made of a device equipped with both imageinformation display means and light irradiating means, i.e., a polymerdispersed liquid crystal given a hologram function.

A conventional polymer dispersed liquid crystal makes a display, makinguse of a light scattering phenomenon caused by both a high polymer andliquid crystal existing as a certain aggregate. In this case, thedistribution state of the liquid crystal and the high polymer is, so tospeak, random.

A large number of propositions have been made of the construction of thepolymer dispersed liquid crystal layer and the fabrication method. Ithas been proposed, for example, in Published Unexamined PatentApplication Nos. H1-142713, H1-225924, H2-99919, and H1-252689, thatliquid crystal is capsuled with a high polymer medium, that liquidcrystal is contained in a porous high polymer, that a high polymer andliquid crystal are emulsified and separated from each other, and that amonomer and a liquid crystal mixture are polymerized with light or heatand are separated from each other. These methods differ from each other,but liquid crystal is dispersed at random into a high polymer matrix,then light is scattered, and a slightly opaque image is obtained. If avoltage is applied to this, then liquid crystal will be regularlyarranged and become transparent. When a reflection display device of adirect visual type is used, light from a suitable light source isirradiated to a scattered and slightly opaque image, and the reflectedlight will be observed. In such a case, the back scatteringcharacteristic of the polymer dispersed liquid crystal layer must begreat with respect to the irradiated light.

When a projection display device is used, an image is constructed bytransparent pixels, but the forward scattering component of the polymerdispersed liquid crystal layer needs to be suppressed because theforward scattering light from some other scattered and slightly pixelsreduces the contrast.

However, a conventional polymer dispersed liquid crystal layer such asdescribed above makes a display, using the light scattering phenomenoncaused by both a high polymer and liquid crystal existing as a certainaggregate, and in this case, the distribution state of the liquidcrystal and the high polymer is, so to speak, random. Therefore, becauseat least 50% of illumination light passes through the polymer dispersedliquid crystal layer as forward scattering light, it is extremelydifficult to enhance the ratio of the back scattering light which isobtained, and yet the ratio cannot exceed 50%.

On the other hand, in the liquid crystal display device of thisembodiment, the distribution state of a high polymer and liquid crystalis controlled so that the back scattering or forward scattering in thedisplay of the polymer dispersed liquid crystal is selectively enhancedoverwhelmingly. That is, the liquid crystal display device of thisembodiment is characterized in that liquid crystal and a high polymerare arrayed in the form of a lattice with a hologram fabricatingtechnique and that light is incident from a fixed light source on thearrayed liquid crystal and light is, so to speak, modulated, whereby ascattering image is obtained. In addition, by selecting the angles ofthe object light and the reference light when fabricating a hologram,the angles of the incident light from a light source at the time ofregeneration and the emitted light from a display can be related to apredetermined relationship. This can be made as the light irradiatingmeans having an optical-path converting function of this embodiment.

Although the light regulating layer of the liquid crystal display devicein this embodiment can be fabricated by some following methods, thecharacteristic features of this embodiment will be described from thepoint of the operating characteristics with respect to a liquid crystaldisplay device obtained as an example by a photopolymerization method.

A general fabrication method of the photopolymerization method is asfollows:

A light regulating layer precursor is composed of the following maincomponents. The main components are at least one kind of ethyleneunsaturated compound and/or suitable oligomer which can be added andpolymerized, a polymerization initiator, a chain moving agent, a lightsensitizer, and at least one kind of nematic liquid crystal. Thiscomposite is sandwiched between two transparent substrates, and thenlight is irradiated, for example, by an exposure system shown in FIG.29. In the figure, 151 is a coherent light source, for example, an argonlaser (λ=514.5 nm), 152 a shutter, 153 a mirror, 158 a mirror or diffusereflector, 159 a diffuse reflector, 154 an object lens, 155 a spacefilter, 156 a collimate lens, 157 a beam splitter, and 160 or 161 asample. The angle of incident light can be arbitrarily set by adjusting158 and 159 respectively. For a beam, a flat wave or spherical wave canbe arbitrarily selected with a suitable lens system. After the settingof the incident angle, the shutter 152 is closed, then a sample isplaced in a place of 160 or 161, and the shutter 152 is opened forexposure. A given energy was equivalent to about 300 to 1000 mJ/cm².After exposure, UV light is irradiated to the whole surface, and heatprocessing may be performed as needed. A liquid crystal thus made wastaken out and was driven as shown in FIG. 30 (case of a reflectiontype). That is, regenerative light was irradiated from a light source123, an a.c. voltage was applied to a panel 162 through electrodes 163,and an observation was made in one direction. As a result, there wasrecognized the phenomenon of the case where the panel becomestransparent and the case where light is strongly scattered back,depending upon the applied voltage. Although the present invention isnot subjected to any limitations for the following guess, theaforementioned effect caused by the light regulating structure where theliquid crystal display of this embodiment is controlled can beconsidered in one idea as follows:

In a case where an image is regenerated by holography, the same light asobject light will be emitted if light is irradiated in the samedirection as reference light. Because, in this embodiment, lightreflected at the diffuse reflector is used as object light, it isconsidered that a pattern caused by the interference between the objectlight and the reference light has been recorded in the light regulatinglayer. If light is incident in this light regulating layer from the samedirection as the reference light, the light regulating layer will emitlight, as if a diffuse reflector is just behind the liquid crystaldisplay and light is being reflected from the reflector. Therefore, inthe case of the diffraction efficiency being 100%, incident light givesthe same effect as the effect that incident light is practicallyscattered nearly 100% backward. As described above, one of thesignificant features of this embodiment is that while a conventionalpolymer dispersed liquid crystal has simply scattered light equally dueto the random structure and has displayed an image based on thescattering, a novel image display function of selectively scatteringlight backward has been realized by controlling the array of the highpolymer and the liquid crystal layer. Of course, it is obvious that, inthe case of a transmission type hologram, light is scattered forward. Inaddition, scattering light may be used in the reference light, and inthis case, the degree of freedom is increased in the direction of theirradiation light at the time of regeneration. A reason consideredconcerning why the panel becomes transparent when a voltage is appliedis because an orientation of liquid crystal is varied by a voltage andtherefore a difference Δn between a refractive index n₁ of a highpolymer phase and a refractive index n2 of a liquid crystal phase haspractically become zero.

The light regulating layer of the liquid crystal display of thisembodiment can be made by using various kinds of methods.

As one of the methods, basically the photopolymerization method of apolymer dispersed liquid crystal is performed in the same way, coherentlight is used as a light source of irradiation, and the method where thevolume phase hologram is made is performed in the same way, aspreviously described. With this, the light regulating layer is made.Also, the light regulating layer can also be made by using so-calledphotosensitive resin, making interference fringes consisting of a resinlayer and an air layer into the resin by performing developmentprocessing, and impregnating these fringes with liquid crystal. A casewhere an optical switch has been made with the latter method has beenreported by Lawrence Domash et al ("Active Holographic Interconnects forInterfacing Volume Storage," SPIE, Vol. 1662, p 211 (1992)). An ethyleneunsaturated monomer of liquid or low melting point, particularly acrylicor metacrylic ester can be used as a monomer suitable for making a lightregulating layer by photopolymerization. These may be, for example, amultifunctional monomer such as trimethylol propane triacrylate, or anoligomer such as ethylene glycol acrylate or urethane acrylate. Thesemay be used individually or can also be used in combination.Furthermore, other monomers such as styrene or carbazole may be usedtogether as needed. These monomers and oligomers are not particularlyspecified, but one usually used for making a polymer dispersed liquidcrystal can be used, or various kinds of monomers or oligomers wellknown to those having skill in this field, such as a photopolymerizationcomposite for making a volume hologram such as that proposed inPublished Unexamined Patent Application No. H2-3082, can be properlyselected and used. In order to make a photopolymerization with coherentlight, sensitizing dyes corresponding to the wavelength and anappropriate photopolymerization initiator are needed, and cyanine dyes,dyes such as cyclopentanone, diphenyl iodonium salt or a combination ofthis salt and dyes, various kinds of quinone, triphenylimidazole dimmer,and hydrogen donor can be suitably selected in combination and used. Itis desirable that liquid crystal be one whose birefringence anddielectric anisotropy is large and whose elastic constant is small, andvarious kinds of liquid crystal already put on the market can beselected and used. For example, the following general equations aredesirable. ##STR1## where R represents the alkyl or alkoxyl group wherethe number of carbons is 2 to 10. These can be mixed according to thepurpose and used.

While the present invention will be described in detail with referenceto embodiments, it is not limited to these embodiments.

(Embodiment-C1)

A mixture, which is composed of 10 parts of ethyl hexyl acrylate, 26parts of trimethylol propane triacrylate, and 5 parts of urethaneacrylate oligomer all as a monomer, 60 parts of the following compositeas liquid crystal, ##STR2## 0.3 parts of 2-mercaptobenzoxazole, 0.25parts of 2,2'-bis(o-chlorophenyl)-4,4',5,5'-tetraphenyl-1,1'-biimidazol, 0.05 parts ofcyclopentanone-2,5-bis {(4-(diethylamino)-phenyl) methylene}, and a verysmall amount of 2,6-di-tert-butylphenol, was inserted between two ITOglass plates of 10 cm×10 cm. In the exposure system shown in FIG. 29, anargon laser (wavelength 514 nm, 100 mW) was used as a light source. AnMgO plate was placed as a diffuse reflector at a position 1 cm away froma sample, and object light and reference light were incidentperpendicular to the sample. With a reflection type, exposure was madefor 15 seconds. Thereafter, the whole surface was exposed with UV light.The obtained liquid crystal exhibited a transmittance of about 77% witha threshold voltage of 35 V, and if white light was irradiated at thetime of nonapplication of a voltage, green back scattering was seen.

(Embodiment-C2)

A liquid crystal panel was fabricated in the same way as theembodiment-C1, except that, as a monomer, ethyl hexyl acrylate is 8parts of the whole, trimethylol propane triacrylate is 10 parts,urethane acrylate oligomer is 3 parts, and liquid crystal is 80 parts.The transmittance was 85% with a threshold voltage of 28 V, and if whitelight is irradiated at the time of nonapplication of a voltage, greenback scattering was seen.

(Embodiment-C3)

A liquid crystal panel was fabricated in the same way as theembodiment-C2, except that as a monomer, the mixed ratio of ethyl hexylacrylate and trimethylol propane triacrylate is 3 parts and 15 parts.The transmittance was 85% with a threshold voltage of 30 V, and greenback scattering was seen at the time of nonapplication of a voltage andwith white light irradiation.

(Embodiment-C4)

A liquid crystal panel was fabricated in the same way as theembodiment-C1, except that, as a monomer, ethyl hexyl acrylate is 3parts, trimethylol propane triacrylate is 21 parts, urethane acrylate is6 parts, and liquid crystal is 70 parts. The transmittance was 87% witha threshold voltage of 40 V, and if white light is irradiated at thetime of nonapplication of a voltage, green back scattering was seen.

(Embodiment-C5)

A liquid crystal panel was fabricated in the same way as theembodiment-C1, except that the MgO plate adheres closely to the sampleand the reference light is also used for the object light and irradiatedwithout using the object light. The transmittance was 75% with athreshold voltage of 33 V, and extremely strong green back scatteringwas seen at the time of nonapplication of a voltage and with white lightirradiation.

(Embodiment-C6)

In the embodiment-C1, if the light source is replaced with red (Kryptonlaser, λ=647 nm) and blue (Argon laser, λ=458 nm), regenerativescattering light can be made red and blue. With the same conditions asthe embodiment-C1, a mask pattern with fine holes, such as that shown inFIG. 19, is placed on the surface of the ITO glass plate on the objectlight side. First, exposure is performed with green laser light, andthen the mask is shifted by one pitch and exposure is performed with ared laser. Furthermore, the mask is shifted and exposure is performedwith a blue laser. UV whole-surface exposure processing is performed inthe sample thus exposed in sequence to the whole surface of the panel.It is considered that the regenerative pattern will become such apattern as shown in FIG. 20. The white strong scattering reflectionlight was obtained with white light irradiation to the obtained panel.

(Embodiment-C7)

A panel was made in the same way as the embodiment-C6, except that themask pattern of the embodiment-C6 is formed into a square hole (1-cmsquare, for example) as shown in FIG. 32. When white light wasirradiated to the obtained panel, there was recognized color scatteringlight where red, blue, and green are independently obtained at everypattern.

The aforementioned hologram is not limited to these embodiments, but adisplay of color by various patterns is possible by using an arbitrarypattern mask.

(Embodiment-C8)

A panel was made in the same way as the embodiment-C7, except thatreference light is incident from the end face of the substrate at anangle near 90 degrees relative to the surface direction. Whenregenerative white light was incident upon the obtained panel in thesame direction as the reference light, i.e., from the panel substrateend face, the same scattering light as the embodiment-C7 was obtained.

While the aforementioned embodiments have been described with referenceto the reflection hologram, of course the transmission hologram is alsopossible, and it is obvious in this case that strong forward scatteringis selectively obtained. In addition, in the case of polychromaticprinting, it is also obvious that a plurality of lasers are irradiatedto the sample at the same time so that superimposed printing can bemade.

As described above, a device equipped with both image informationdisplay means and light irradiating means becomes possible according tothis embodiment, and the HUD of this embodiment can be made as a morecompact form. In addition, the scattering selectivity of the HUD isenhanced also as a polymer dispersed liquid crystal, so a brighter imageis obtained at a wide visual field angle.

(D)

While the structure of the polymer dispersed liquid crystal has beencontrolled so that scattering can be selectively performed and the lightutilization efficiency could be improved, the scattering efficiency waslower than one predicted at the beginning. For example, in the polymerdispersed liquid crystal of the back scattering mode, it was found thatslight forward scattering was still included. This is considered to bebecause the self-interference of the scattered laser light takes placewhen fabricating the hologram and, as a result, unnecessary noisegrating is printed.

When laser light is irradiated on a diffusing surface at the time ofhologram fabrication to try to obtain scattering light, a mutualself-interference such as that shown in FIG. 33 will take place. In thefigure, two very small areas adjacent to the diffusing surface areschematically shown. The scattering light from each very smallscattering surface element is emitted from the diffusing surface andthen meets the scattering light from another very small scatteringsurface element, and forms interference fringes at that position. Now,if a light regulating layer precursor composed of the liquid crystalphase and the high-polymer phase of this embodiment is put at theposition shown by a broken line of FIG. 33, the aforementionedinterference fringes will be recorded as a refractive index profile.This is referred to as a noise grating. If illumination light isirradiated to the aforementioned hologram on which the noise gratingsare recorded or the aforementioned light regulating layer, as shown inFIG. 34, light is randomly scattered due to each grating. Because thedirection is oriented on the side opposite to the incident side of theillumination light, this becomes forward scattering light. In FIG. 34,it is assumed that light is incident from one direction as illuminationlight, but in a case where natural light or scattering illuminationlight such as a general room illumination is incident, more randomforward scattering light will occur and this will cause a reduction inthe picture quality of the liquid crystal display.

It has been found that an occurrence of this noise grating can besuppressed by making hologram patterns with certain improved specialscattering-light.

With FIG. 35, the noise-grating suppressing operation will be describedwith a special scattering-plate of this embodiment taken as an example.It is assumed that two very small scattering areas of the specialscattering-plate each have a size of "w" and are arranged at a certaininterval of "p". The horizontal line in the central portion in thefigure represents the film thickness of a volume hologram, which issupposed to be disposed in contact with the special scattering-plate.From the geometrical relationship between the film thickness and thescattering light beam from each very small scattering area, symmetricalscattering light beams from both the very small scattering areas make anangle of 30 degrees measured from the scattering surface with respect toa film thickness t1, while the symmetrical scattering light beams become45 degrees with respect to a film thickness t2. Interference occursbetween the scattering light beams included in these scattering angles.However, assuming perfect diffusing light, a quantity of light includedin these scattering angles is 1/16 for 30 degrees and only 1/4 even for45 degrees. Most light beams other than this portion do not cross eachother within the volume hologram and do not contribute to formation of anoise grating. By introducing reference light, a hologram will beindependently formed between this main scattering light and referencelight.

(Embodiment-D1)

The structure control of the polymer dispersed liquid crystal layer ofthis embodiment is realized with a fabricating method describedhereinafter. FIG. 36 is an example of an optical system for fabricatingthe polymer dispersed liquid crystal layer 162' (FIG. 30) of thisembodiment. A light regulating layer precursor 167 is interposed betweenthe surfaces of transparent substrates 164 and 165 on which transparentelectrodes 163 are formed. The transparent substrates both were glassplates of thickness 1.1 mm, the transparent electrodes both werepatterned ITO films, and the thickness of the light regulating layerprecursor was about 3 micron. 168 is a special scattering-plate, verysmall scattering areas 169 are formed on the glass plate in a mosaicmanner, and a reflecting film 170 is formed on the remaining flatportion. The size of the very small scattering areas is about 50 micronand the interval is about 0.5 mm. This is formed by coating aphotoresist on an aluminum deposited glass plate, giving theaforementioned mosaic pattern to the coated plate by photolithography,removing the aluminum film from the resist removed portion by etching,and furthermore giving sand blasting to the exposed glass surface of theetched portion. If argon ion laser light 171 of linear polarization isirradiated with a wavelength of 458 nm to this special scattering-plate168, light passing through the very small scattering area 169 will berandomly scattered and object light 172 where this small scattered lightbeams are arranged in the form of a mosaic will be obtained. Because thelaser light 171 incident upon the area other than the very smallscattering areas 169 is reflected by the reflecting film 170, the laserlight will not be contained in the object light 172. This object lightis incident from the side of the transparent substrate .164, whilereference light 173 of the same laser light is incident from the side ofthe transparent substrate 165. Laser light irradiation of about 50mJ/cm² is performed, and at the time the aforementioned polymerizationprocess has been advanced, the irradiation of the laser light isstopped. Then, uniform ultraviolet light is irradiated to the lightregulating layer precursor 167, the entire is sufficiently polymerized,and the process is completed.

It was found that the polymer dispersed liquid crystal layer, fabricatedin a method such as this, reflected and scattered illumination light ofnearly 458 nm at efficiency exceeding 90% and could be observed in awide angle range. A clear boundary was not seen between the areas wherethe very small scattering areas was placed when fabricating and theremaining area, and scattering light was observed over nearly the entiresurface. The pixel to which a voltage of about 30 V was applied becametransparent.

While in this embodiment the special scattering-plate, provided withvery small scattering areas of transmission types at part of thereflecting surface thereof, has been used, a special scattering-plate174 where a reflecting film is provided only on a very small scatteringarea, shown in FIG. 37, may be used and laser light may be reflected atthis surface. In addition, it is also possible to use a specialscattering-plate whose entire surface is a transmission type or areflection type.

Also, while in this embodiment the hologram pattern has been formed withthe special scattering-plate closely contacted, the object light may beformed by forming an image of a scattering surface by the use of lensesor by a two-step exposure method. In addition, while in this embodimentthe reference light has been collimated light, a uniform and wide visualangle can be realized by using the scattering light produced by auniform scattering surface or the special scattering-plate of thisembodiment as reference light. Furthermore, the object light may beformed by a pin hole array or a combination of a pin hole array and ascattering plate instead of the special scattering-plate.

(Embodiment-D2)

This embodiment is the same as the embodiment-D1, except that thestructure of the polymer dispersed liquid crystal layer differs. In thestructure of this polymer dispersed liquid crystal layer, thedistribution state of the liquid crystal phase and the high-polymerphase is controlled as a reflection hologram pattern, and this structurecontrol is realized by a fabricating method described hereinafter. Thatis, as shown in FIG. 38, scattering light in the relationship where aP-wave and a S-wave are adjacent to each other as reference light isused to fabricate a hologram between the scattering light and the objectlight. The scattering light of these P-wave and S-wave adjacent to eachother can be easily obtained by dividing a single laser beam into aS-wave and a P-wave by a 1/2 wavelength plate, passing these wavesthrough masks (a) and (b) whose positions are complemented with eachother, such as that shown for example in FIG. 39, to synthesize them asshown in (c), and passing the synthesized wave through a scatteringplate.

In FIG. 38, the light regulating layer precursor 167 is interposedbetween the surfaces of the transparent substrates 164 and 165 on whichthe transparent electrodes 163 are formed. The thickness of the glassplates of the transparent substrates were both 1.1 mm, the transparentelectrodes both were patterned ITO films, and the thickness of the lightregulating layer precursor was about 3 micron. The size of the masktransmission pattern is about 50 micron and the interval is about 1.0mm. Argon ion laser light of wavelength 458 nm was used as laser light.The object light 178 is caused to be incident from the side of thetransparent substrate 164, while the reference light 173 is caused to beincident from the side of the transparent substrate 165. The objectlight and the reference light cause an interference pattern, and in thelight regulating layer precursor 167, photopolymerization is started atthe portion whose interference light intensity is high and then ahigh-polymer phase of a three-dimensional structure is formed. Laserlight irradiation of about 30 mJ/cm² is performed, and at the time theaforementioned polymerization process has been sufficiently advanced,the irradiation of the laser light is stopped. Then, uniform ultravioletlight is irradiated to the light regulating layer precursor 167, theentire is sufficiently polymerized, and the process is completed.

It was found that the fabricated polymer dispersed liquid crystal layerreflected and scattered illumination light of nearly 458 nm atefficiency exceeding 90% and that it had a uniform wide visual angle invertical and lateral directions. The pixel to which a voltage of about30 V was applied became transparent.

(Embodiment-D3)

FIG.40 shows part of a n optical system for fabricating a polymerdispersed liquid crystal layer of a liquid crystal display device ofthis embodiment. In this embodiment, the angle of laser light 184 whichis incident upon a pin hole array 183 is varied in a time series manneras shown in (a), (b), and (c) of FIG. 40, and then weak hologrampatterns are formed with the object light 185 passed through the pinhole array at the set angles and reference light 173. In FIG. 40, threedirections of (a), (b), and (c) have been shown for the sake ofconvenience. In practice, these weak hologram patterns are multiplexedin the light regulating layer precursor 167 with respect to all desireddirections covering the angle of view of the display device, wherebyscattering light with respect to illumination light is regenerated.According to this method, coherence can be eliminated in point of time.Therefore, hologram patterns are formed without interfering to eachother and formation of noise gratings is suppressed.

While, in this embodiment, the pin hole array which is a fine patternhas been fixed and the angle of the laser light which is incident uponthis array has been varied, a similar result would be obtained, even iflaser light which is scattering light were incident upon the pin holearray and the position of the pin hole array were scanned. Incorrespondence with this, it is desirable that incident reference lighthave at least enough size to cover the fine pattern, and incidentreference light is scanned in synchronization with object light.

(Embodiment-D4)

FIG. 31 shows a liquid crystal display device in this embodiment. Thisembodiment is the same as the embodiment-D1, except that the structureof a polymer dispersed liquid crystal layer 188 differs. For thispolymer dispersed liquid crystal layer 188, initially a hologram patternis made by laser light of wavelength 458 nm, using a mask having apattern such as that shown in FIG. 19. Then, the mask is shifted by onepitch and a hologram pattern is made by laser light of wavelength 514nm. Finally, the mask is further shifted by one pitch and a hologrampattern is made by laser light of wavelength 648 nm. In this way, thelayer 188 is formed. Each pattern is aligned with the position of atransparent electrode constituting a pixel, and pixels of "R,""G," and"B" are arrayed in the form of a mosaic, as shown in FIG. 31. Thepolymer dispersed liquid crystal layer 188 constructed in this way isseen as a white scattering surface, judging from the appearance.However, if a voltage is applied to each pixel so that the transmittanceis varied, three colors of red, green, and blue will be observed. Withthis, it was found that a color image could be constituted.

(E)

In a case where a volume phase hologram in this embodiment is used as alight irradiating means, various usable modes become possible dependingupon the direction of light diffracted by the hologram. A descriptionwill hereinafter be made of some examples.

(Embodiment-E1)

FIG. 41 is a diagram of a HUD constructed according to this embodiment.The HUD is constituted by a combination of a polymer dispersed liquidcrystal display device 145, a cold cathode fluorescent tube 192, areflecting mirror 193, a cylindrical lens 194, a transparent substrate195, and a hologram 196.

This polymer dispersed liquid crystal display device 145 displays animage with the forward scattering of the liquid crystal layer. The lightemitted from the cold cathode fluorescent tube 192 is focused once bythe reflecting mirror 193, is converted into collimated whiteillumination light 197 by the cylindrical lens 194, and is incident onthe transparent substrate 195. This collimated light becomes diffractedillumination light 198 which is emitted from the surface by the hologram196, and illuminates the polymer dispersed liquid crystal display device145. The hologram 196 is a so-called edge-lit hologram of the volumephase type constructed so that only light incident on the edge surfaceof the transparent substrate 195 can be emitted to the outside of thesubstrate. The hologram 196 is transparent in appearance, because nodiffracted illumination light 198 is formed due to the diffraction ofthe light incident on the surface of the transparent substrate 195.Therefore, if the polymer dispersed liquid crystal display device is setto the transparent state, the entire image display portion of thedisplay device will become transparent, and the background can be viewedlike a scene seen through a glass. In addition, because the hologram isconstructed such that the diffracted illumination light 198 is emittedfrom the surface in the down direction, there is no possibility thatunnecessary illumination light passing through the transparent area ofthe polymer dispersed liquid crystal display device enters directly intothe eyes of an observer. Therefore, since only the pixel 199 in thescattering state is brightly seen to the observer, an image superimposedwith the background, whose contrast is high, is displayed. The hologramof this embodiment is constructed so as to meet the following Equations:

    n sin |α|>1                        (Eq. 1)

    n sin |β|<1                         (Eq. 2)

    n sin |2α+β-π|>1           (Eq. 3)

where n is the refractive index of the hologram medium, α and β are theincident angle of the reference light and the incident angle of theobject light, defined in the hologram medium, and π is the ratio of thecircumference of a circle to its diameter. Equations 1 and 2 representthe condition where light is incident on the end surface of the hologramsubstrate and becomes illumination light that is emitted from thehologram surface. Also, Equation 3 represents the condition for assuringthe monochromaticity of the illumination light. FIG. 42 shows thatreference light 200, incident from the end surface of a transparentsubstrate 195, interfere within the hologram medium with object light201 and that a hologram 196 of a cycle structure is formed. If the whiteillumination light 197 is incident at the same angle as the incidentangle of the reference light 200 and is regenerated, then seconddiffracted light 206 will coexist because incident light other thantarget diffracted light 204 will be all reflected at the hologramsurface. In order to prevent this, the angle of emission ν of the seconddiffracted light 206, 2α+β-π, can be made so as to meet atotal-reflection condition such as that shown in Equation 3.

(Embodiment-E2)

This embodiment is used as the reflection type where dichroic dyes arecontained in polymer dispersed liquid crystal. FIG. 43 shows a partschematic view of the structure of this embodiment (transparentelectrode and glass substrate not shown). The light emitted from a lightsource 123 is diffracted by a hologram 213 and gets into the liquidcrystal panel portion. In an ON portion 212 (transparent), a liquidcrystal layer 215 containing dichroic dyes is oriented and transparent,and the incident light is absorbed by a back absorbing plate 211 anddoes not return. On the other hand, for the light that got into an OFFportion 210 (scattering), light with a certain wavelength is absorbedand the remaining light is scattered and dyed, by the dyes in liquidcrystal 214 of non-orientation. If a volume phase hologram is used forthe hologram, light with a particular wavelength can be selectivelydiffracted. If the intensity of a light source becomes stronger, abrighter image can be obtained. For example, if a blue dye (dyeabsorbing light other than a blue color) is used and diffracted light ofblue color is selected, the light will be scattered without beingabsorbed in the OFF portion. Because the hologram is transparent whenviewed from the scattering side, a bright blue image is displayed on ablack ground. Even if external light were superimposed on this and theabsorption of the dyes were slightly incomplete, an image whose contrastis sufficiently strong would be obtained by diffracted light. If the HUDof this embodiment is used in the sunvisor of an automobile, it will beuseful.

(Embodiment-E3)

FIG. 44 shows a case where this embodiment is used as the transmissiontype where a dichroic dye is contained in polymer dispersed liquidcrystal. The light emitted from a light source 123 is diffracted at ahologram 196 in an oblique direction. In a scattering portion 220 at anOFF state, a bright blue image is displayed because light is scatteredat the image portion independently of the incidence direction ofdiffracted light. In an ON portion 221, blue diffracted light isobliquely incident on the image portion and does not get into the eyes.Therefore, only external light gets into the eyes and the ON portion istransparently seen. Even if external incident light (external light) gotinto, only the light of the OFF portion would be enhanced by thediffracted light. Therefore, an image whose contrast is high is obtainedalso with this case. It is obvious that other colors, for example,green, red, and yellow colors can be used.

In the following embodiments, a normal reflection liquid crystal panelis used as an image information display means. Although a normalreflection liquid crystal panel has a reflecting plate at the backthereof, an image does not become bright so much, because surroundinglight is used as illumination light. When this is combined with lightirradiating means using the hologram of this embodiment, a very brightimage is obtained. If the HUD of this embodiment is used in the sunvisorof an automobile, it will be useful.

(Embodiment-E4)

FIG. 45 shows a case where a transmission hologram has been placed atthe front of a liquid crystal panel. In the figure, 230 is atransmission hologram, 123 a light source, 232 liquid crystal, 233 aglass plate provided with transparent electrodes or a filter, and 234 areflecting plate. The incident light from the light source 123 isdiffracted at the hologram and illuminates the liquid crystal from thefront. The diffracted light is reflected at the reflecting plate 234 anda bright image is observed. In FIG. 46, a hologram previously made on atransparent substrate 241 is attached to a reflection liquid crystalpanel 240. In FIG. 46(a) a transmission hologram 242 is shown, and inFIG. 46(b) a reflection hologram 243 is shown.

(Embodiment-E5)

FIG. 47 (a) shows a case where, in the embodiment-E4, a reflectionhologram 252 is placed at an angle in advance. In this case, all that isrequired of a light source 123 is to emit light only upward, and thelight source is released from slight angle adjustment. In order to placethe hologram at an angle, the cross section of a transparent substrate251 may be formed into a triangle, or a thin transparent substrate maybe obliquely placed. Also, as shown in FIG. 47(b), in a case where lightis irradiated from a light source 123 to a transparent substrate 261,the surface is cut so that light is all reflected. Therefore, thereflected light reaches a transparent hologram 262, and is diffracted inthe liquid crystal panel direction. In addition, as shown in FIG. 47(c),in an example where a transparent hologram 272 is reversed and placedobliquely, a light source 123 is placed at the vertex of the triangularhologram. The light, irradiated just upward from the light source 123,is diffracted at the hologram 272 and is irradiated in the liquidcrystal direction. The cross section of the transparent substrate may beformed into a triangle, or a thin substrate may be placed at an angle.These structures are also useful.

Industrial Applicability

As has been described above, the present invention is a head up displayunit which comprises: transparent and flat image information displaymeans; transparent and flat light irradiating means arranged in anopposed and close contact relationship with the image informationdisplay means; light supply means for supplying light to the lightirradiating means; image-display control means for controlling imagedisplay; and light-supply control means for controlling light supply.The display unit may be constructed such that the image informationmeans and the light irradiating means are combined with each other. Thedisplay unit can be used in any place in the interior of an automobileand is a substantially transparent and compact head up display unitwhere optical and illumination systems are integrated with each other.

We claim:
 1. A head up display unit comprising:transparent and flatimage information display means having a front surface; transparent andflat light irradiating means, said light irradiating means between saidimage information display means and a user; light supply means forsupplying light to a surface of said light irradiating means, said lightirradiating means reflecting said light from said front surface of saidimage information display means; image-display control means forcontrolling an image display of said image information display means;and light-supply control means for controlling the light supply of saidlight supply means.
 2. The head up display unit as set forth in claim 1,wherein said transparent and flat image information display means is oneselected from a group of a liquid crystal panel, a polymer dispersedliquid crystal panel, and a ferroelectric thin film.
 3. The head updisplay unit as set forth in claim 1, wherein said light irradiatingmeans has optical-path converting means for emitting incident lightwhich was incident from said light supply means arranged on part or allof the peripheral end face of said light irradiating means, in a surfacedirection of said light irradiating means.
 4. The head up display unitas set forth in claim 3, wherein said optical-path converting means isone selected from a group of a volume phase hologram, a phasediffraction grating comprising asymmetrical unevenness, and a halfmirror.
 5. The head up display unit as set forth in claim 4, whereinsaid optical-path converting means is a volume phase hologram having aplurality of sections, and at least a first section of the saidplurality of sections is different than a second section of saidplurality of sections.
 6. The head up display unit as set forth in claim1, wherein said light supply means is a light source itself emittinglight, such as various kinds of lamps, a discharge tube,electroluminescence, a plasma illuminant, a light emitting diode, and alaser, or is a phosphor and a light source which excites said phosphor.7. The head up display unit as set forth in claim 1, wherein said lightsupply means is provided with a light source and an optical fiber forguiding light from said light source.
 8. A head up display unit, whereinthe head up display device as set forth in claim 1 is placed on adashboard of an automobile, has a drive portion which can be pulled downbefore and after, and is fixed at an arbitrary angle.
 9. A head updisplay unit, wherein the head up display device as set forth in claim 1is fixed by freely rotatable fixing tool attached to the upper portionof a windshield of an automobile and is pulled down to the windshieldsurface when it is used.
 10. A head up display unit, wherein the head updisplay device as set forth in claim 1 is placed in the vicinity of arear window of an automobile and displays image information to theoutside.
 11. A head up display unit, wherein the head up display deviceas set forth in claim 1 is part or all of a windshield of an automobile.12. A head up display unit, wherein the head up display device as setforth in claim 1 is part or all of a rear window of an automobile. 13.The head up display unit as set forth in claim 1, wherein said lightfrom said light supply means is free of traveling through said imageinformation display means.
 14. The head up display unit as set forth inclaim 1, wherein said light supply means is directly facing said imageinformation display means.